The present invention relates generally to an adhesion promoting layer for a transparent metal oxide layer on a substrate, and more particularly, to a metal adhesion and IR reflection layer for UV absorbing metal oxide coated polymeric windows.
Car manufacturers have traditionally used glass as the material for car windows. However, recently it has become desirable to substitute glass windows with polymeric windows, such as polycarbonate (PC) windows. Polymeric windows are often advantageous compared to glass windows because of their low weight, high strength and ease of shaping. However, some polymeric windows, such as PC windows, turn yellow after being exposed to the ultraviolet (UV) radiation in sunlight. The yellow windows suffer from poor transmission of visible light, thus making them unsuitable for many car window applications.
One solution to the UV damage problem is to coat the polymeric substrates with a TiO2 (titanium dioxide) layer. The TiO2 coating acts as a partial absorber of UV radiation, and provides a measure of protection for some applications. However, TiO2 generally provides an insufficient amount of UV absorption, and windows coated with TiO2 eventually turn a shade of yellow. TiO2 is also a photocatalyst for oxidation of polymers. Therefore, TiO2 coated polymers are generally unsuitable as a car window material.
Another solution to the UV damage problem is to coat the polymers with a ZnO (zinc oxide) layer. Zinc oxide provides a greater amount UV absorption than TiO2. Therefore, polymers coated with ZnO generally do not turn yellow when exposed to sunlight. However, prior art ZnO coatings are known to dissolve in water. Poor water soak stability on many substrates, including polycarbonate (PC), has thus surfaced as one potential limitation to the use of ZnO as a UV absorber for car windows, because car windows are frequently exposed to rain and snow.
In view of the foregoing, it would be desirable to provide a UV absorption layer for transparent substrates which provides a high UV absorption rate as well as good weather stability. A method of making a metal oxide layer that has good adhesion strength to a transparent substrate would also be desirable.
The present invention provides a substrate, a transparent metal layer on the substrate, and a transparent metal oxide layer.
The present invention also provides a window usable in a vehicle, building, apparatus, or display device, for example, comprising a polycarbonate base material, an infrared (IR) radiation reflection layer comprising aluminum or silver, and an ultraviolet (UV) radiation absorption layer comprising, for example, ZnO, indium doped zinc oxide (IZO) or aluminum doped zinc oxide (AZO).
The present invention also provides a method of coating a substrate, comprising the steps of forming a transparent metal layer on the substrate, and forming a transparent metal oxide layer on the metal layer.